1. Field of the Invention
The present invention relates to the technical field of fingerprint recognitions and, more particularly, to an electronic device with fingerprint recognition circuit powered by dedicated power source.
2. Description of Related Art
With the development of electronic commences, remote payments are getting more and more popular and thus the requirement for biometrics is highly increased. The biometrics technology can be divided into fingerprint recognition, iris recognition, DNA recognition, and the like. For the efficient, safe, and non-intrusive considerations, the fingerprint recognition becomes the first selected technology.
In terms of the recognition principle, the fingerprint recognition can be classified into optical scanning, thermal image sensing, and capacitive sensing and, upon consideration of the cost, power-saving, reliability, and anti-counterfeit, the capacitive sensing is the outstanding one.
Typically, in terms of the recognition operation, the fingerprint recognition can be divided into the types of linear swiping scan and full area detection, wherein the full area detection is better due to its resolution, efficiency, and convenience. However, due to the factors that the sensing signal is very weak and the background noise is complicated and strong, the fingerprint recognition of full area detection is typically implemented by forming the sensor electrodes and the sensing circuit in one IC chip with a sapphire film having a thickness of smaller than 100 μm for protection. Such material cost and package cost are quite high. Accordingly, the manufacturing cost is extremely high, and the product's lifetime and tolerance are suspicious. Thus, the industry has attempted to increase the sensing sensitivity and the signal to noise ratio (SNR) for placing a fingerprint recognition sensing device beneath a protective glass, even into a display panel, so as to cost down and increase the product's lifetime and tolerance.
FIG. 1A is a schematic diagram of a typical capacitive fingerprint signal sensing. As shown, a plurality of sensing electrodes 11 is disposed on a substrate 10 in columns and rows to perform a capacitance sensing, and the electrical signals sensed by the sensor electrodes 11 are transmitted through the corresponding conductive wires 12 for output, so as to obtain a fingerprint image. Such a single-layer transparent electrode structure can realize fingerprint recognition. In use, the single-layer transparent electrode structure of FIG. 1A is combined with a display panel. However, when the single-layer transparent electrode structure of fingerprint recognition is integrated to the inside of a display panel, there will be an obvious capacitance produced between the single-layer transparent electrode structure and a common voltage (Vcom) layer of the display panel, which may cause noises to be produced and thus lower the accuracy in fingerprint recognition. Therefore, it is known that the fingerprint recognition circuit is highly susceptible to noises, and accordingly its design has to avoid the noise interference as much as possible.
FIG. 1B is a schematic diagram illustrating how a fingerprint recognition circuit is interfered by noise. As shown, in an electronic device such as a smart phone, a fingerprint recognition circuit chip 13 is connected to a sensor electrode 15 through a conductive wire 14 for sensing analog signal generated by a finger's touch. In addition, a microprocessor 16 in the electronic device is connected to another circuit chip 18 or the fingerprint recognition circuit chip 13 through a connection wire 17 in order to transmit digital signal for providing a corresponding function of the electronic device. Since the electronic devices tend to be compact, the conductive wire 14 and the connection wire 17 are typically very close to each other. Moreover, the fingerprint recognition circuit chip 13, the microprocessor 16, and the another circuit chip 18 in the electronic device are powered by a single battery power source. As a result, the analog signal of the conductive wire 14 is likely to be interfered by the control signal of the connection wire 17, resulting in an error on fingerprint recognition.
Therefore, it is desirable to provide an improved fingerprint recognition circuit to an electronic device to mitigate and/or obviate the aforementioned problems.